Solid polymer fuel cells are expected as new energy sources since they utilize chemical reaction between oxygen and hydrogen and therefore are environmentally-friendly. Technical development of such fuel cells has been promoted.
As a hydrogen supply source for a fixed-type solid polymer fuel cell, hydrogen gas, which is obtained by means of reforming of hydrocarbon (reformed gas), may be used. However, it is known that such reformed gas contains a trace amount of carbon monoxide (CO) as a side reaction product. This CO strongly adsorbs to the surface of a platinum catalyst, which is used as an electrode, resulting in poisoning. The problem had been that platinum's catalyst activity for hydrogen oxidation is inhibited thereby (M. Watanabe, S. Motoo, J. Electroanal. Chem., 60, 267 (1975)).
In order to prevent such CO poisoning, Pt—Ru binary-type alloy has been conventionally used as an electrode catalyst having resistance to CO poisoning. However, in general, the upper limit of CO concentration is about 200 ppm, and therefore, resistance to CO poisoning of the binary-type alloy is still insufficient. For this reason, when using an electrode catalyst utilizing Pt—Ru binary-type alloy, a unit for shift reaction and selective oxidation reaction, which reduces CO concentration in reformed gas, is required. This has been a major reason for high production costs of fixed-type fuel cells.